232 



THE CIRCULATION OF THE BLOOD 



tains no nervous mechanism and its behavior may be safely attributed to 

 the muscle substance itself. 



Try the following experiments: Submit the strip to saline solutions of 

 different temperatures, varying through steps of 5 degrees from o C. to 

 40 C. Try the effect of the different ingredients in Ringer's solution; com- 

 bine potassium with saline, figure 172; calcium with saline, figure 173; and 

 potassium, calcium, and saline. Also try Locke's solution; solution of blood 

 diluted with saline; solution of milk with saline in the proportion of one 

 part milk to four of saline. 



Cut and mount strips from the auricle and from the sinus, letting 

 the latter extend out on to the vena cava. In these last preparations 

 care must be taken to balance the lever, as a slight overtension paralyzes 

 the muscle. Immerse these strips in pure serum, compare their behavior 



FIG. 215. Arrangement of Apparatus for Studying the Contractions of the Strip of the Apex 



of the Ventricle. 



with that of the ventricle in pure serum. The sinus and usually the auricle 

 will be found rhythmic in serum, while the ventricle, if it contracts at all, 

 will contract with a very slow rhythm. Often there is a distinct progressive 

 decrease in the rhythm, the sinus having the same rhythm as the whole heart, 

 the auricle a considerably slower rhythm, and the ventricle with a very slow 

 rhythm or even quiet. The sinus preparation will show beside the funda- 

 mental rhythm a characteristic slow contraction and relaxation, which has 

 been described as tone, figure 170. 



10. Influence of the Cardiac Nerves on the Frog's Heart. Care- 

 fully pith a frog so as not to break the blood-vessels at the base of the brain, 

 and thus permit the loss of the blood of the animal. Expose the heart as 

 previously described, make a cut through the manubrium, continue it througn 



